Electrical power components, such as capacitors, bushings, and instrument transformers, comprise a condenser core arranged in, surrounded by an electrically insulating housing. The condenser core includes at least one conductor extending along a longitudinal axis of the housing and an electrical insulation surrounding the conductor. The electrical insulation surrounding the conductor is, for example, made of wounded paper impregnated with oil. A space is formed between the condenser core and the housing. The space between the condenser core and the housing contains an insulating fluid to impregnate the insulation surrounding the conductor. The insulating fluid is usually oil. During operation and/or when the ambient temperature of the power component is increasing, the temperature of the oil is increased and by that the volume of the oil is increased. In order to avoid increased pressure in the housing when the temperature of the oil is increased, the power component is provided with an expansion vessel positioned adjacent and in open communication with the space between the condenser core and the housing. There is an open gap between the expansion vessel and the condenser core. The expansion vessel is at least partially filled with a compressible gas volume, which is in direct contact with the surface of the oil. When the volume of the oil increases, the increased volume of the oil is expanded into the expansion vessel and the gas is compressed.
A disadvantage with such a power component is that during transportation and storage, when the component is held in a horizontal position due to its length, a part of the oil flows into the expansion vessel and the position of the gas volume is moved in the expansion vessel. This may cause the oil level in the housing to reach below the winded insulation surrounding the conductor. A consequence of this is that the insulation of the condenser core is exposed to gas from the expansion vessel, which may cause damage of the impregnation of the winded insulation of the condenser core. If the power component is taken into operation too quickly after it has been raised and before it has been fully impregnated, partial discharge (PD) can occur. This can drastically decrease the life time of the component or even destroy the component right away. This can be an even bigger problem if it is the only spare component on site. Also, if it is a spare component, there is often a big hurry to get the transformer going again. The quantity of the PD activities is often very small, which makes it hard to measure. Because of this, an oil impregnated component needs to be vertically mounted for several days before it is re-impregnated, and safe to take into operation again.
One solution to this problem is to arrange the expansion vessel asymmetrically in relation to the condenser core. A disadvantage with this solution is that the oil will flow into the expansion vessel and the insulation of the condenser core will not be covered with oil if the component is turned upside down when it is held in a horizontal position.
GB1 445 025 discloses an electrically insulated bushing, whereby gas that is present in the housing above the level of the insulation oil, is prevented from dissolving in the oil by using closed compressible gas container in the housing. These containers are wound around the conductor inside the housing. The housing can be filled with oil, and the gas container can be filled with gas from an exterior of the bushing. This is a complex and rather expensive solution to the problem and there is always a risk that leakage can occur between the gas volume and the oil volume.